Sod harvesters have been commercially available for a long time, and usually are designed as self-propelled machines or as a cutting unit which can be attached to a conventional tractor. In either case, the harvester has a cutting head which includes (a) a generally-horizontal knife to undercut the sod at a specified depth, (b) side cutting blades or coulters to cut the edges of the sod strip, and (c) a roller to support the weight of the cutting head and to establish the thickness of the sod strip. Cut strips of sod are delivered onto a conveyor which conveys the strips rearwardly and upwardly away from the cutting head, for collection.
Sod harvesters have used a variety of methods to follow the contour of the ground; in general, the objective is to allow the operator to cut a thin strip of sod without the risk of scalping, or cutting too thinly on occasion. Some harvesters, commonly referred to as “conventional” or “fixed head” harvesters, have the cutting head rigidly connected to the conveyor frame. Examples of this type of harvester are the harvester described in U.S. Pat. No. 3,540,535, the Brouwer model 1555, and the Kesmac model 2100. These harvesters include a pivoting “ball joint” connection at the rear of the conveyor, which allows the cutting head to rise and fall with undulations in the direction of motion of the harvester. A “track rod” connects the cutting head or conveyor to the tractor with pivoting ball joints and holds the cutting head parallel to the direction of motion. These pivot joints also allow the conveyor and cutting head frame to rock from side to side to follow undulations perpendicular to the direction of motion of the harvester. The axis about which the conveyor and cutter assembly rotates is defined by the location of the centres of the rear pivot point and the track rod connection to the cutting head or conveyor. Since this axis is not horizontal, the cutting knives turn away from being exactly perpendicular to the direction of travel when the head pivots, resulting in damage to the edges of the sod strip.
This problem is addressed by harvesters that are commonly referred to as “floating head”, or “pivoting head”, harvesters, which have a pivoting connection between the cutting head frame and the conveyor frame. U.S. Pat. Nos. 4,621,696, 3,807,504, and 4,892,152 disclose harvesters of this type, in which the cutting head can tilt about a horizontal pivot axis. The cutting knives and roller no longer pivot front-to-back. However, since the axis of tilt lies at some distance above ground level, the cutting head can be induced to pivot by a side load on the knives and roller, such as would happen if sod is being cut on a curve, as is common with center-pivot irrigation sod cultivation. This can result in scalping.
One attempt to solve the floating head problem is disclosed in U.S. Pat. No. 6,112,825. This patent describes a floating head design in which the pivoting connection between the cutting head and the conveyor is angled, such that the pivot axis intersects the knife. It should be noted, however, that a side load on the knives and roller can induce the whole assembly to pivot on an axis defined by the front and rear support ball joints, causing scalping.